| Objectives:Weight loss and cachexia are common problems in colorectal cancer(CRC)patients;The incidence of malnutrition is high up to 39.3%,thus parenteral and enteral nutrition(PEN)support play important roles in cancer care.However,the impact of nonessential amino acid components of nutritional intake on cancer progression has not been fully studied.Therefore,this project aims to assess the impacts of nonessential amino acids in nutrition support on clinical outcomes of gastrointestinal cancer,to screen the key amino acid that affect the prognosis of patients,and further analyze their functions as well as clarify the underline mechanisms,and ultimately help optimizing the nutritional support formula for CRC patientsMethods:In order to screen the key amino acid components that affect the survival and prognosis of CRC patients,this project retrospectively reviewed the records of patients with gastrointestinal cancer who received parenteral nutrition support(PN)from 2008 to 2013 in MD Anderson Cancer Center(n=1378),the results showed that cysteine,aspartic acid,and glutamate in PN are associated with poor survival in patients with gastrointestinal cancer,and demonstrated that cyst(e)ine has an unique and effective function in promoting CRC by a series of in vivo and in vitro experiments.Firstly,this study performed SRB assay and xenografting experiment to verify the impact of cyst(e)ine nutrient on cell viability,drug sensitivity and tumor growth;We then used flow cytometry and EdU assay to detect the effect of cystine on cell cycle distribution,cell apoptosis and DNA synthesis;After that,we clarified the mechanism by which cyst(e)ine promotes colon cancer growth and chemoresistance by RNA-seq,WB,qRT-PCR and ROS/GSH detection,and used small molecule inhibitors and siRNAs to perform rescue experiments.At last,this study used conditional media that lacking different amino acids to compare the difference between cystine and several other non-essential amino acids deprivation on CRC cell survival and chemotherapy sensitivity.Results:The results of the first part of this study found that:patients who received cysteine as part of the parenteral nutrition had shorter overall survival(P<0.001)than those who did not.Cystine indeed robustly promotes colon cancer cell growth in vitro and in immunodeficient mice,cystine promotes colon cancer cell cycle progression and DNA synthesis;Importantly,dietary deprivation of cystine suppresses colon cancer xenograft growth without weight loss in mice.The results of the second and third parts of this study analyzed the mechanism by which cystine promotes colon cancer cell growth:The underline mechanism is that cystine predominately inhibits SESN2 transcription via suppressing GCN2-ATF4 axis,resulting in mTORC1 activation.Both depletion of mTOR or using mTORC1 inhibitors rapamycin/everolimus block cystine-induced cancer cell proliferation.The results of the fourth part of this study indicate that cystine confers resistance to oxaliplatin and irinotecan,the main mechanism is that cystine helps colon cancer cells to quench chemotherapy-induced reactive oxygen species via synthesizing glutathione,thereby protecting colon cancer cells from chemotherapy-induced apoptosis,leading to chemotherapy resistance;Cystine deprivation diet significantly boosts the antitumor effect of oxaliplatin in colon cancer xenografts.Finally,this study also compared cystine with other non-essential amino acids including leucine,lysine,or arginine.Compared to amino acids complete media(AAs+)media,cell viability was attenuated when deprivation any one of these amino acid,but cystine or arginine deprivation showed the most significant inhibition effect.However,surprisingly,upon oxaliplatin treatment,only cystine deprivation increased colon cancer cell chemosensitivity,oxaliplatin-caused cell growth inhibition and oxaliplatin-induced apoptosis were further increased by deprivation of cystine rather than leucine,lysine,or arginine,indicating that cystine has a more important and unique role in CRC,and cystine in PEN leads to poor prognosis in CRC patients.Conclusions:These findings indicate that cyst(e)ine as part of supplemental nutrition plays an important role in colorectal cancer,and manipulation of cyst(e)ine content in nutritional formulations may optimize colorectal cancer patient survival. |
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